1. Field of the Invention
This invention relates to a new energy attenuation apparatus for a system conveying a liquid under pressure and to a method of attenuating energy in such a system. The invention is particularly suitable for placement in a system conveying liquid under pressure for the attenuation of pressure pulsations in the liquid, especially in the hydraulic system of the power steering unit of a vehicle. The invention would also be suitable for other hydraulic fluids.
2. Prior Art Statement
In hydraulic systems where the operating liquid is circulated by a pump, the pulsations of pressure that are generated by the pump are transmitted through the conduits and result in noise and/or vibration being produced by the hydraulic liquid. In the case of power steering fluid in vehicles, such noise and/or vibration is caused, for example, when vehicles are being parked or unparked at idle or very low speeds of movement thereof, such as by barely moving into and out of a parking space or the like while the wheels of the vehicle are being turned by the power steering mechanism thereof. In particular, substantial noise and/or vibration (shudder) can be produced in such a situation when the power steering fluid passes through the power steering mechanism from the fluid pump to the effective steering structure. Further background in this area can be obtained from U.S. Pat. No. 3,323,305, Klees, whereby this U.S. Patent is being incorporated into this disclosure by this reference thereto.
Devices are known for suppressing noise in exhaust gas mufflers. For example, U.S. Pat. No. 4,501,341, Jones, provides two side branch resonators, while U.S. Pat. No. 4,371,053, Jones, provides for an apertured tube in a gas muffler housing. Systems are also known for controlling the resonation of pressure waves in fuel injection systems. For example, U.S. Pat. No. 5,168,855, Stone, passes fluid through check valves that are provided with a flow restriction either directly therein or in a bypass line. U.S. Pat. No. 5,509,391, DeGroot, provides a spool valve assembly for controlling flow between inlet and outlet ports. Henderson et al, U.S. Pat. No. 4,671,380, discloses a long and narrow tubular casing having a perforated tube extending therethrough. "Acoustics of Ducts and Mufflers", by M. L. Munjal, provides a resonator for conveying gas in the form of an apertured tube disposed in a tubular cavity. Finally, U.S. Pat. No. 5,539,164, van Ruiten, discloses a power steering attenuation hose construction that utilizes wound or coiled metal tuning cables.